Conventionally, there is known a normal incidence telescope for observing light of a predetermined energy, which comprises a reflecting mirror, on the surface of which a multilayer film is formed and which reflects only light of a predetermined energy corresponding to the multilayer film at high reflectance, and a detector such as a semiconductor detector to which reflected light reflected by the reflecting mirror is condensed and which detects the light of a predetermined energy.
On the other hand, in the astronomic observation, since an apparent energy level considerably fluctuates due to collective motion and red shift, light is not observed in an energy band anticipated in rest system. A multilayer film of a conventional reflecting mirror has a narrow band in which only light of a predetermined energy is reflected at high reflectance, so that discovery of line spectrum in a celestial body, which fluctuates remarkably, is not expected.
Specifically, in the above-described astronomic observation, a telescope capable of observing the light in a broad energy band is desired. Particularly, since a complex index of refraction is approximately 1, and δ(=1−n) and extinction coefficient K is sufficiently smaller than 1 in a region extending from extreme ultraviolet ray to x-ray, a reflectance of normal incidence does not reach 1% in bulk. Besides, because light in a region extending from extreme ultraviolet ray to x-ray is absorbed by atmospheric air, a telescope capable of performing observation outside aerosphere is desired.
However, in the conventional normal incidence telescope, the multilayer film formed on the surface of the reflecting mirror exhibits high reflectance only to light of a predetermined energy, only the light of a predetermined energy reflected at high reflectance by the reflecting mirror can be observed, on which the multilayer film was formed, and there has been a problem that observation could not been performed with respect to light in a broad energy band which is the light in a region extending from visible light to x-ray, for example.
Further, in the conventional normal incidence telescope, single telescope can only observe the light of a predetermined energy corresponding to the multilayer film of the reflecting mirror, it is required to use a plurality of normal incidence telescopes each having the reflecting mirror on which the multilayer film reflecting light of different energy is formed in order to observe the light in a broad energy band by the conventional normal telescope. As a result, a new problem such as cost increase and securing of a wide space for arranging a plurality of normal incidence telescopes occurs.
Furthermore, when a plurality of the conventional normal incidence telescopes are used so as to have the reflecting mirrors on which the multilayer films reflecting light of different energy are formed, it is required to control a plurality of the normal incidence telescopes, there existed a problem of reduction of efficiency.
On the other hand, an oblique incidence optical system is known for obtaining high reflectance with respect to the region extending from visible light to x-ray, but the oblique incidence optical system has had various problems such as a narrow field of vision and a small effective area.
The present invention has been made in view of the above-described problems involved in prior art, and its object is to provide a broadband telescope that utilizes the advantages of the normal incidence optical system and the oblique incidence optical system well to make it possible to observe light in a broad energy band.
Further, another object of the present invention is to provide a broadband telescope in which a composite telescope of the normal incidence optical system and the oblique incidence optical system reflects each light rays in a broad energy band extending from visible light to x-ray, for example, at high reflectance to achieve cost reduction and space saving and to make it possible to efficiently observe the light in a broad energy band.